The incident occurred between junctions five (Maidstone) and six (Eastbourne) heading clockwise on Thursday morning.
Photos showed the vehicle spewing black smoke into the air as emergency services raced to the scene.
Both lanes one and two were closed while the emergency services deal with the blaze.
A National Highways spokesperson said previously: "Traffic has now been released in lanes 3 and 4 on the #M25 clockwise between J5 (#M26) and J6 (#Godstone) following a vehicle fire. "Lanes 1 and 2 remain closed while recovery and carriageway assessment crews continue to work at scene." At the time of writing, drivers were told to expect delays of up to 60 minutes.
A later update added that "lanes 1 and 2 will be closed throughout the rest of the morning for resurfacing".
Kent Fire and Rescue added: "Two fire engines attended and crews wearing breathing apparatus extinguished the flames using hose reel jets and compressed air foam.
"No injuries were reported."
